A leading proponent of California‘s Proposition 8, whose whose writings linked homosexuality to pedophilia and prostitution, was called to the stand as a “hostile witness” Thursday by plaintiff’s attorneys, aimed at showing that hostility and animus toward gays and lesbians fueled the passage of the voter-approved ban on gay marriage.

Hak-Shing William Tam, director of the Traditional Family Coalition and a proponent of Prop. 8, testifying in the trial challenging Prop 8, held fast to his view that allowing same-sex couples to marry would bring about “moral and societal decay.”

In the months leading up to the November 2008 vote, Tam warned of the disastrous consequences of allowing gays to marry in California, and worked to mobile the Asian community in favor of Prop. 8.

“One by one, other states would fall into Satan’s hands,” Tam wrote in a letter to Chinese-American churchgoers. “Every child, when growing up, would fantasize marrying someone of the same sex. More children would become homosexuals.”

Tam testified that he believes homosexuality to be linked to pedophilia, and that homosexuals are 12 times more likely to molest children, and cited “different literature” he had read to support his conclusion, none of which he could recall in response to questioning by plaintiffs attorney David Boies.

“I believe if the term marriage can be used beyond one man, one woman, then any two persons of any age, of any relationship, can use the same argument to come and ask for the term marriage. That would lead to incest. That would lead to polygamy. If this is a civil right, what would prevent other groups form asking for the same right.”

Under questioning by Boies, Tam said Protect Marriage had invited him to be an official proponent, counseled him speaking points, and wrote a declaration he signed saying he had supervised preparation of the text of the ballot measure.

Tam collected signatures, organized rallies and raised money for the campaign in the Asian American community, stayed in contact with Protect Marriage leaders and signed a “statement of unity” in July 2008 promising to coordinate all messages with the campaign committee, Tam said.

“I was playing a major role” in the Prop. 8 campaign, he said.

But during cross-examination, Prop 8 lawyer Nicole Moss, through her questions, tried to distance the campaign from Tam’s statements, depicting him as going rogue with his statements about gays and lesbians without the consent of Proposition 8 campaign officials.

“I was acting independently,” Tam said of statements he made that were not approved by ProtectMarriage.com and Proposition 8’s leadership.

Boies followed-up in redirect by showing a series of e-mails and other evidence that linked Tam to the campaign and ProtectMarriage.com leaders, and noted that he was directly involved in organizing rallies against same-sex marriage — an effort to debunk the defense’s claim that Tam was acting alone.

Tam was one of the five official sponsors of Proposition 8 who formally “intervened” in the federal lawsuit challenging Proposition 8. The lawsuit, Perry v. Schwarzenegger, officially names the state of California as the defendant, but Gov. Arnold Schwarzenegger and Attorney General Jerry Brown have refused to defend the voter-approved ban.

Earlier this month, Tam asked to be removed from the lawsuit over fear the trial publicity that would endanger him and his family. But U.S. District Judge Vaughn Walker, presiding over the non-jury trial, ruled Thursday that it was unfair “to join a lawsuit and then just decide to withdraw,” finding it “prudent to hear Tam’s testimony.”

The trial resumes in federal court in San Francisco Friday with the plaintiffs final witness, psychology professor Greg Herek, who is expected to testify about the nature of homosexuality.